Sound insulation materials are used in a variety of settings where it is desired to dampen noise from an external source. For example, sound insulation materials have been used in applications such as in appliances to reduce the sound emitted into the surrounding areas of a home, in automobiles to reduce mechanical sounds of the motor and road noise, and in office buildings to attenuate sound generated from the workplace, such as from telephone conversations or from the operation of office equipment. In automobiles, the insulation material also relies upon thermal shielding properties to reduce or prevent the transmission of heat from various heat sources in the automobile (e.g., engine, transmission, exhaust, etc.) to the passenger compartment of the vehicle. Acoustical insulation typically relies upon both sound absorption (i.e., the ability to absorb incident sound waves) and transmission loss (i.e., the ability to reflect incident sound waves) to provide adequate sound attenuation.
Conventional acoustical insulation materials include materials such as foams, compressed fibers, fiberglass batts, felts, and nonwoven webs of fibers such as meltblown fibers. Laminates of one or more layers of insulation and one or more layers of a rigid material are commonly used when a rigid insulative material is desired. Examples of conventional acoustical insulation materials are set forth below.
U.S. Pat. No. 5,662,981 to Olinger et al. describes a molded composite product that has a resinous core layer that contains reinforcement fibers (e.g., glass and polymer fibers) and a resinous surface layer that is substantially free of reinforcement fibers. The surface layer may be formed of thermoplastics or thermoset materials such as poytretrafluoroethylene, polyethylene terephthalate (PET), polyvinyl chloride (PVC), polyphenylene sulfide (PPS), or polycarbonate.
U.S. Pat. No. 5,886,306 to Patel et al. discloses a layered acoustical insulating web that includes a series of cellulose fiber layers sandwiched between a layer of melt-blown or spun-bond thermoplastic fibers (e.g., polypropylene) and a layer of film, foil, paper, or spunbond thermoplastic fibers.
U.S. Pat. No. 6,669,265 to Tilton et al. describes a fibrous material that has a lofty, acoustically insulating portion and a relatively higher density skin that may function as a water barrier. The fibrous material includes polyester, polyethylene, polypropylene, polyethylene terephthalate (PET), glass fibers, natural fibers, and mixtures thereof.
U.S. Pat. No. 6,695,939 to Nakamura et al. discloses an interior trim material that is formed of a substrate and a skin bonded to the substrate. The substrate is a mat-like fiber structure that is a blend of thermoplastic and inorganic fibers. The skin is a high melting point fiber sheet formed from fibers that have a melting point higher than the melting point of the thermoplastic fibers in the substrate. The high melting point fibers may be polyethylene terephthalate (PET) fibers.
U.S. Patent Publication No. 2003/0039793 A1 to Tilton et al. describes a trim panel insulator for a vehicle that includes a nonlaminate acoustical and thermal insulating layer of polymer fibers. The insulator may also include a relatively high density, nonlaminate skin of polymer fibers and/or one or more facing layers formed of polyester, polypropylene, polyethylene, rayon, ethylene vinyl acetate, polyvinyl chloride, fibrous scrim, metallic foil, and mixtures thereof.
U.S. Patent Publication No. 2004/0002274 A1 to Tilton discloses a laminate material that includes (1) a base layer formed of polyester, polypropylene, polyethylene, fiberglass, natural fibers, nylon, rayon, and blends thereof and (2) a facing layer. The base layer has a density of from approximately 0.5-15.0 pcf and the facing layer has a density of between about 10 pcf and about 100 pcf.
U.S. Patent Publication No. 2004/0023586 A1 to Tilton et al. and U.S. patent Publication No. 2003/0008592 to Block et al. disclose a fibrous blanket material that has a first fibrous layer formed of polyester, polypropylene, polyethylene, fiberglass, natural fibers, nylon, and/or rayon and a layer of meltblown polypropylene fibers. A second fibrous layer may be sandwiched between the first fibrous layer and the layer of meltblown fibers. The blanket material may be tuned to provide sound attenuation for a particular product application.
U.S. Patent Publication No. 2004/0077247 to Schmidt et al. describes a nonwoven laminate that contains a first layer formed of thermoplastic spunbond filaments having an average denier less than about 1.8 dpf and a second layer containing thermoplastic multicomponent spunbond filaments having an average denier greater than about 2.3 dpf. The laminate has a structure such that the density of the first layer is greater than the density of the second layer and the thickness of the second layer is greater than the thickness of the first layer.
Although there are numerous acoustical insulation products in existence in the art, none of the existing insulation products provide sufficient structural properties for automotive applications. Thus, there exists a need for acoustical insulation materials that exhibit superior sound attenuating properties, improved structural and thermal properties, and that are lightweight and low in cost.